1. Field of the Invention
The present invention relates to a device for rapidly fixing blades onto the shafts of wood planers, with which it is proposed to solve in the most satisfactory, practical and cost-effective manner the problem of rapidly changing said blades when they are worn.
2. Description of the Prior Art
The shafts are of the type having formed, along their peripheral surface, longitudinal, straight or helical recesses, each of which houses, as shown by way of example in FIGS. 1 and 2 of the accompanying drawings, a blade 1 and prism-shaped locking bar 2 with counter-tightening screws 3 which press against the locking bar in a direction tangential to the shaft.
In shafts of this type, the operation of changing the blades is somewhat difficult and laborious since it involves loosening all the screws 3, replacing the blade 1 and then tightening again all the screws 3, so as to fix the blade in position again. Since there are about ten screws for each blade, the operation also requires a lot of time. If this constitutes a drawback of a not insignificant nature it can be easily understood that it becomes a very serious problem in the case of wood planer shafts which, according to the most common current trend in the sector, envisage the use of disposable blades instead of the more traditional blades which must be resharpened and adjusted in position on the shaft. In fact the efficiency and productivity of planers with disposable blades is strictly dependent upon the speed of replacing said blades.
The object of the present invention is therefore that of eliminating the abovementioned drawback by replacing, in the shafts of planers, the large number of screws used for tightening the locking bar which fixes the blades, with a rapid system which has a single central operating member.
The present invention constitutes an improvement to a prior patent in the name of the same inventor (Italian application No. 19989 A/90 filed on 11 Apr. 1990) with the same object, in which the toggles were formed by a spring steel bar folded sinusoidally or by separate diamond-shaped struts. This solution had the drawback, however, that there was a non-uniform radial pressure on the locking bar due to the sliding friction which the toggles encountered during their axial movement with an increase in the radial pressure.
The present invention aims to eliminate the abovementioned drawback by means of toggles consisting of rollers arranged with their axes staggered in succession as described below.
More precisely the present invention relates, in a blade-holding shaft for planers of the type where the peripheral surface has, formed along it, longitudinal recesses each housing a working blade and a prism-shaped locking bar, to an element for rapidly fixing said blades, characterized in that it comprises a series of roller-type toggles housed in succession in a recess parallel to and radially inside the recess housing the blade and the locking bar, and a central operating member able to exert an axial thrust on the toggles at the two free ends of the recess so as to produce, on the locking bar, a radial thrusting force for each toggle in the series.